feat(DRC-2081): implement frontend idle detection mechanism

[iamcxa]

Implements a hybrid idle detection system to prevent unexpected server timeouts when users are actively using the application.

Backend changes:

• Add POST /api/keep-alive endpoint to reset idle timer
• Expose idle_timeout field in /api/instance-info response
• Add debug logging for keep-alive requests

Frontend changes:

• Add RecceInstanceInfo.idle_timeout field in TypeScript interface
• Create sendKeepAlive() API client with error handling
• Implement useIdleDetection hook with the following features:
  • Monitors multiple activity types (focus, mousemove, keydown, scroll)
  • Dynamic debounce interval: idle_timeout / 3 (clamped 30s-5min)
  • Tab awareness using Page Visibility API (pauses when inactive)
  • Lock mechanism prevents concurrent API calls
  • Activity log throttling (max 1 log per second)
  • Dev-only logging (disabled in production builds)
• Integrate IdleDetector component in app Providers

Key implementation details:

• Uses optimistic locking to prevent race conditions
• Updates lastActivityRef before API call to prevent duplicate sends
• Only activates when server has idle_timeout configured
• Automatically adapts debounce interval to server configuration
• Immediately sends keep-alive when tab becomes active after 5+ minutes

🤖 Generated with Claude Code

PR checklist

• [ ] Ensure you have added or ran the appropriate tests for your PR.
• [ ] DCO signed

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[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
recce/server.py	50.89% <100.00%> (+0.89%)	:arrow_up:
tests/test_server.py	100.00% <100.00%> (ø)

... and 5 files with indirect coverage changes

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[Copilot]

@iamcxa I've opened a new pull request, #971, to work on those changes. Once the pull request is ready, I'll request review from you.

[iamcxa]

@copilot open a new pull request to apply changes based on the comments in this thread

[Copilot]

@iamcxa I've opened a new pull request, #972, to work on those changes. Once the pull request is ready, I'll request review from you.